According to my local service men I should be able to turn about 4600
RPMs with my 5.0 liter mercruiser. I am only turning 4200 at full
throttle, on plane and empty except for drive and one passenger. My
service guys say I can burn the valves at this rate.

What say you all?

Elevation of test, about 4000 feet above sea level, 5.0 liter Cobalt
21 foot open bow, 450 hours on engine.

Thanks in advance for any helpful info.